321
FXUS02 KWBC 130711
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
311 AM EDT Thu Aug 13 2026

Valid 12Z Sun Aug 16 2026 - 12Z Thu Aug 20 2026


...Hazardous Heat in the South-Central and Southeast U.S...

...Heavy Rain Threats for the Southwest, Central Plains, Midwest,
Northeast and Mid- Atlantic through early next week...


...Overview...

The broad and persistent upper ridge across the southern tier
continues to bring hazardous heat across the south-central U.S.
and Southeast into next week, while a relatively active northern-
stream flow remains established from the northern Rockies/Plains
into the Great Lakes and Northeast. This will facilitate multiple
rounds of showers and thunderstorms that may lead to flash
flooding. Meanwhile, a upper trough will push into the West Coast
bringing chances for unsettled weather across portions of north-
western U.S. while monsoonal moisture will continue to bring heavy
rainfall across the Southwest into the central Plains.


...Guidance/Predictability Assessment...

The latest model guidance continues to support good confidence in
the placement of the southern U.S. ridge and the persistence of the
periodic shortwave energy across the northern tier. Uncertainty
grows in regard to the timing, amplitude, and the interaction of
individual shortwaves with frontal boundaries and the developing
trough over western U.S. The GFS seems to be faster with some of
the features that eject into the West, which will impact
precipitation maxima, while the CMC seems a bit slower, especially
towards mid- week. With higher confidence of a slower moving
trough, the forecast initially weighted a even multi-model blend,
while phasing out the deterministic models by early next week and
incorporating the ensemble means for the remainder of the
forecast.



...Weather/Hazards Highlights...


The strong upper ridge remains positioned over the southern U.S.
and will maintain anomalous warm temperatures from the southern
Plains through the Lower Mississippi Valley, Tennessee Valley, and
Southeast. Afternoon temperatures will commonly reach the upper
90s to lower 100s across the interior South, while high humidity
and persistent elevated dew points will produce oppressive heat
indices of 105-115 degrees. Record- breaking warm overnight
temperatures will further limit recovery, particularly where
several consecutive days of heat occur. Widespread Major to
Extreme HeatRisk conditions will remain possible into next week.
Several consecutive days of high heat stress can lead to heat-
related illnesses.

Monsoonal moisture will traveling northward, bringing a active
pattern across the western and central U.S. through next week. The
deep subtropical moisture will continue to circulate around the
western periphery of the southern- tier ridge, supporting
recurring thunderstorms across portions of the Southwest into the
central Rockies/Plains. Slow storm motions may lead to localized
heavy rainfall. Repeated convection will maintain a risk for flash
flooding, especially over burn scars, steep terrain, slot canyons,
and urbanized areas. This is highlighted in the WPC Excessive
Rainfall Outlook (ERO) for Day 4/Sunday and Day 5/Monday where
there is a Marginal Risk across portions of the Four Corners and
central Plains, with a Slight Risk over portions of Colorado for
Day 4. Further north, an upper trough digging southward off the
West Coast is expected to become increasingly influential toward
the middle of next week. Although there is still some uncertainty
on the evolution of this feature, chances for shower and
thunderstorms increases for the Great Basin and the northern
Rockies as the trough moves eastward.

The moist and unstable air mass will remain positioned ahead of a
series of northern-stream disturbances. Frontal boundaries and
surfaces waves interacting with the anomalous moisture will support
repeated rounds of showers and thunderstorms across the Midwest,
Ohio Valley/Mid-Atlantic, Great Lakes, and Northeast on Sunday.
With the combination of high low-level moisture and instability,
training thunderstorms may develop, which can lead to flash
flooding, especially over areas where soils remain saturated from
previous rainfall. This is highlighted by a Marginal Risk over
parts of these regions on the Day 4/Sunday ERO, with a Slight Risk
over portions of Mid-Atlantic and Northeast.

On Monday, the surface low and associated boundary, continues to
push northeast, as the trailing front moves southward across the
Ohio/Tennessee Valley into the Mid-Atlantic and the Northeast
coast. Continuous interactions with warm, moist, unstable airmass
along the boundary may lead to organized convection and excessive
rainfall. Meanwhile, another upper- level disturbance will bring
multiple rounds of thunderstorms and showers across the Northern
Rockies/Plains into the Upper Midwest and will linger through mid-
week. Therefore, Day 5/Monday ERO highlights the flood risk across
the Mid-Atlantic and portions of the northern Plains and Upper
Midwest. Otherwise, showers and thunderstorms push into the
Southeast On Tuesday as the frontal system dips further south.



Oudit



Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast, excessive rainfall outlook,
winter weather outlook probabilities, heat indices and Key Messages
are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw








$$